1. Field of the Invention
This invention relates to a heat-sensitive recording material excellent in storage stabilities of image area and uncolored area produced by providing a specified heat-sensitive recording layer on a support.
2. Prior Art
Heat-sensitive recording materials are generally produced by providing a heat-sensitive recording layer composed mainly of an electron-donative colorless dye precursor and an electron-acceptive color developing agent on a support. When it is heated by means of thermal head, thermal pen, laser light or the like, the colorless dye precursor and the color developing agent instantaneously react to form a record image. They are disclosed in Japanese Patent Publication No. 43-4,160, Japanese Patent Publication No. 45-14,039, etc. This type of heat-sensitive recording materials are advantageous in that they can make a record with a relatively simple apparatus, their maintenance is easy to practice, and they emit no noises. Thus, they are utilized in wide fields such as recorders for measurements, facsimiles, printers, computer terminals, labels, ticket vending machines and the like.
Although this type of heat-sensitive recording materials using an electron-donative colorless dye precursor and an electron-acceptive color developing agent have many excellent properties such as good appearance, good touch, high optical density of developed color, diversity in the hue of developed color, and so on, they are disadvantageous because of poor storage stability of image. For example, if the record image area is contacted with a plastic material such as polyvinyl chloride, it disappears due to the action of plasticizer or other additives present in the plastic material, or it readily disappears upon contact with the chemicals used in foodstuffs or cosmetics, or it readily disappears when exposed to sunlight only for a short period of time. Because of this disadvantage, their use is limited at the present stage, and their improvement in this point is intensely desired.
As heat-sensitive recording material wherein two components mutually react upon heating to form a record image of good storage stability, heat-sensitive recording materials wherein the two components consist of an imino compound and an isocyanate compound are disclosed in, for example, Japanese Patent Application Kokai (Laid-Open) Nos. 58-38,733, 58-54,085, 58-104,959, 58-149,388, 59-115,887 and 59-115,888, as well as in U.S. Pat. No. 4,521,793.
Although the heat-sensitive recording materials excellent in record storability consisting of an isocyanate compound and an imino compound are excellent in record storability of image, they are disadvantageous in that the non-image area (ground area) can be colored when contacted with plasticizer or the like.